High voltage bushings are used for carrying current at high potential through a plane, often referred to as a grounded plane, where the plane is at a different potential than the current path. Bushings are designed to electrically insulate a high voltage conductor, located inside the bushing, from the grounded plane. The grounded plane can for example be a transformer tank or a wall, such as for example a High Voltage Direct Current (HVDC) valve hall wall.
In order to obtain a smoothening of the electrical potential distribution between the conductor and the grounded plane, a bushing often comprises a condenser core. A condenser core is a body which typically comprises a number of floating, coaxial foils made of a conducting material, where the foils are separated by a dielectric spacing material, which could for example be oil impregnated or resin impregnated paper. Examples of bushings comprising a condenser core are disclosed in patent document EPI 798740.